The present invention relates to microelectromechanical systems devices, and more particularly, to drive circuitry for microelectromechanical systems devices and other applications.
Microelectromechanical systems (MEMS) devices are used in a variety of applications. For example, MEMS devices have been used as variable optical attenuators and dynamic filters in fiber-optic communications equipment. MEMS devices are typically based on one or more miniature movable silicon or silicon-based elements. Semiconductor microfabrication techniques may be used to fabricate MEMS devices.
The position of the movable elements in a MEMS device may be controlled electrostatically using controllable DC drive voltages. It may sometimes be preferred to use AC drive voltages rather than DC drive voltages to reduce drift effects due to unwanted accumulations of charge in portions of the MEMS device. With this approach, the polarity of the voltage that is applied to the MEMS device is continually reversed, but the position of the movable elements may still be controlled by adjusting the magnitude of the drive voltage. The frequency of the AC signal is typically selected to be high enough to avoid creating any undesirable mechanical resonances.
Drive circuits that produce AC signals may also be used in other applications such as applications involving the control of electrical, mechanical, and optical components and test and measurement applications.
It is an object of the present invention to provide circuitry that produces AC signals having a controllable magnitude.
It is also an object of the present invention to provide drive circuits for microelectromechanical system devices.
These and other objects of the invention are accomplished in accordance with the present invention by providing circuitry that produces AC output signals. The AC output signals may be used as drive signals to control the operation of microelectromechanical systems (MEMS) devices. For example, the circuitry may be used to provide AC drive signals for controlling the operation of MEMS devices used in fiber-optic communications networks.
The AC signals that are produced may have a controllable magnitude. The frequency of the AC signals may be on the order of 100 KHz to 10 MHz or any other suitable frequency. The AC signal waveform may be a square wave or any other suitable waveform.
The circuitry may include a controllable DC voltage source. Waveform generator circuitry may use the DC voltage from the voltage source to produce an AC voltage signal with a controllable amplitude. The waveform generator circuitry may be AC coupled to a transformer, so that only the single controllable voltage from the DC voltage source needs to be used to produce the controllable-amplitude AC voltage signal. The transformer may boost the amplitude of the AC voltage signal so that the boosted signal may be used as a drive signal for a microelectromechanical systems device or other device. The transformer may be housed in a relatively small package such as a surface mount package. A control unit may be used to control the voltage of the drive signal.
Circuitry that generates multiple AC drive signals in parallel may be provided. A control unit may be used to individually control each of the AC drive signals. Multiple DC voltage sources may be used to create individually-controllable DC voltages. Waveform generator circuitry may be provided to convert each of the DC voltages into a corresponding AC voltage signal. The magnitudes of the AC voltage signals may be boosted by transformers. Multiple transformers may be housed in a single package. For example, multiple transformers may be housed in a single DIP-style package. Each AC drive signal may be used to control a different movable or controllable element in a MEMS device.
Further features of the invention and its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.